chromium/third_party/blink/manual_tests/compositing/resources/editable-compositing-subframe.html

<style type="text/css" media="screen">
    #editable {
        height: 100px;
        transform: translateZ(0px);
    }
</style>
<div id="editable" contenteditable="true">
The caret should blink correctly when editing this paragraph.
</div>